This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The function of articular cartilage is to withstand high pressure, absorb shock and prevent the transmission of stress to the underlying bone. Osteoarthritis is a very common disease characterized by progressive degeneration of articular cartilage experienced as pain and disability. Early arthritis is typified by loss of the proteoglycan (PG) "springs" that allow for cartilage to absorb everyday mechanical stress. In the past, it has been shown that both T1[unreadable] relaxation and sodium concentration mapping by magnetic resonance imaging is sensitive to the concentration of proteoglycan in tissue. The purpose of this study is to correlate T1[unreadable] relaxometry with sodium concentrations in arthritic cartilage removed during knee replacements. These results will enable us to determine the specificity of T1[unreadable] MRI towards PG. Sodium MRI, with extensive signal averaging in ex vivo tissue, gives us the ability to generate high resolution, sameslice maps that are impossible to generate in vivo. These results are then compared with histology to make a clear correlation between MRI and histological findings. With these studies we hope to gain additional insight into the spatial distribution and progressive loss of PG in arthritis. These insights will be useful for the tracking of osteoarthritis and its treatments in affected patients. Future goal is to get co-registered sodium and T1[unreadable] In vivo images for detecting early Osteoarthritis for increased diagnostic reliability.